`slicing` an array does NOT allocate memory

content

type sliceHeader struct {
    Data *elem  // pointer to the underlying array
    Len  int
    Cap  int
}

func f() {
    a := []int{1, 2, 3, 4, 5}
    b := a[1:4]
}

Stack:
  a: { ptr → [1 2 3 4 5], len=5, cap=5 }
  b: { ptr → [2 3 4],     len=3, cap=4 }
 
Heap:
  [1 2 3 4 5]

a and b are separate variables on the stack, both pointing to the same data on the heap
stack memory is allocated during function f starts
- so within the function, when b := a[1:4] is called, it only creates new sliceHeader structure in the stack itself
- no memory allocation!
that’s why slice in Go is cheap!

slicing operation does not need to allocate memory, not even for the slice header

research!rsc: Go Data Structures